Coordinate Measuring Machines (CMM)

Coordinate Measuring Machines (CMM) are mechanical systems designed to move a measuring probe to determine coordinates of points on a work piece surface.  CMMs are comprised of four main components: the machine itself, the measuring probe, the control or computing system, and the measuring software.  Machines are available in a wide range of sizes and designs with a variety of different probe technologies.

Important specifications for coordinate measuring machines are the measuring lengths along the x, y and z axes as well as resolution and workpiece weight.  The x-axis measuring length is the total travel, or measuring length that can be performed in the x-direction.  The y-axis measuring length is the total travel, or measuring length that can be performed in the y-direction.  The z-axis measuring length is the total travel, or measuring length that can be performed in the z-direction.  These are not necessarily the same as the measuring capacity, which is the maximum size of the object in the x, y or z-direction that the machine can accommodate.  The resolution is the least increment of a measuring device; on digital instruments, the least significant bit (Reference: ANSI B-89.1.12).  The workpiece weight is the mass of the work piece being measured.

Coordinate measuring machines may have manual control, CNC control or PC control.  Manual control implies that machine positioning is operator controlled.  A Computer Numerical Control (CNC) may also control machine positioning.  PCs or personal computers also control machine positioning in some coordinate measuring machines. 

Operation for a coordinate measuring machine can be achieved through an articulated arm, bridge, cantilever, gantry or horizontal arm.  An articulated arm is very common for portable, or tripod mounted style machines.  The articulating arm allows the probe to be placed in many different directions.  In bridge style machines, the arm is suspended vertically from a horizontal beam that is supported by two vertical posts in a bridge arrangement.  The machine x-axis carries the bridge, which spans the object to be measured. In cantilever style machines, a vertical arm is supported by a cantilevered support structure.  Gantry style machines have a frame structure raised on side supports so as to span over the object to be measured or scanned.  Gantry machines are similar in construction to bridge style designs.  In horizontal arm machines, the arm that supports the probe is horizontally cantilevered from a movable vertical support.  As a result, this style is sometimes referred to as cantilever.

Coordinate measuring machines can have one of several mounting options.  They include benchtop, free standing, handheld and portable.  Manufacturers may use these terms interchangeably.  Probe systems for CMMs can be touch probe or discrete point, laser triangulation, camera or still and video camera.  Further information for CMM probes can be found by searching for CMM Probes on GlobalSpec.  A multi-sensor coordinate measuring machine has capabilities to mount more than one sensor, camera, or probe at a time.

Common applications for coordinate measuring machines include dimensional measurement, profile measurement, angularity or orientation, depth mapping, digitizing or imaging, and shaft measurement.  Features common to CMMs include crash protection, offline programming, reverse engineering, shop floor suitability, SPC software and temperature compensation.

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